Spinal cord injury
A spinal cord injury is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions.
Symptoms of spinal cord injury may include loss of muscle function, sensation, or autonomic function in the parts of the body served by the spinal cord below the level of the injury. Injury can occur at any level of the spinal cord and can be complete, with a total loss of sensation and muscle function at lower sacral segments, or incomplete, meaning some nervous signals are able to travel past the injured area of the cord up to the Sacral S4-5 spinal cord segments. Depending on the location and severity of damage, the symptoms vary, from numbness to paralysis, including bowel or bladder incontinence. Long term outcomes also range widely, from full recovery to permanent tetraplegia or paraplegia. Complications can include muscle atrophy, loss of voluntary motor control, spasticity, pressure sores, infections, and breathing problems.
In the majority of cases the damage results from physical trauma such as car accidents, gunshot wounds, falls, or sports injuries, but it can also result from nontraumatic causes such as infection, insufficient blood flow, and tumors. Just over half of injuries affect the cervical spine, while 15% occur in each of the thoracic spine, border between the thoracic and lumbar spine, and lumbar spine alone. Diagnosis is typically based on symptoms and medical imaging.
Efforts to prevent SCI include individual measures such as using safety equipment, societal measures such as safety regulations in sports and traffic, and improvements to equipment. Treatment starts with restricting further motion of the spine and maintaining adequate blood pressure. Corticosteroids have not been found to be useful. Other interventions vary depending on the location and extent of the injury, from bed rest to surgery. In many cases, spinal cord injuries require long-term physical and occupational therapy, especially if it interferes with activities of daily living.
In the United States, about 12,000 people annually survive a spinal cord injury. The most commonly affected group are young adult males. SCI has seen great improvements in its care since the middle of the 20th century. Research into potential treatments includes stem cell implantation, hypothermia, engineered materials for tissue support, epidural spinal stimulation, and wearable robotic exoskeletons.
Classification
Spinal cord injury can be traumatic or nontraumatic, and can be classified into three types based on cause: mechanical forces, toxic, and ischemic from lack of blood flow. The damage can also be divided into primary and secondary injury: the cell death that occurs immediately in the original injury, and biochemical cascades that are initiated by the original insult and cause further tissue damage. These secondary injury pathways include the ischemic cascade, inflammation, swelling, cell suicide, and neurotransmitter imbalances. They can take place for minutes or weeks following the injury.At each level of the spinal column, spinal nerves branch off from either side of the spinal cord and exit between a pair of vertebrae, to innervate a specific part of the body. The area of skin innervated by a specific spinal nerve is called a dermatome, and the group of muscles innervated by a single spinal nerve is called a myotome. The part of the spinal cord that was damaged corresponds to the spinal nerves at that level and below. Injuries can be cervical 1–8, thoracic 1–12, lumbar 1–5, or sacral. A person's level of injury is defined as the lowest level of full sensation and function. Paraplegia occurs when the legs are affected by the spinal cord damage, and tetraplegia occurs when all four limbs are affected.
SCI is also classified by the degree of impairment. The International Standards for Neurological Classification of Spinal Cord Injury, published by the American Spinal Injury Association, is widely used to document sensory and motor impairments following SCI. It is based on neurological responses, touch and pinprick sensations tested in each dermatome, and strength of the muscles that control key motions on both sides of the body.
Muscle strength is scored on a scale of 0–5 according to the table above, and sensation is graded on a scale of 0–2: 0 is no sensation, 1 is altered or decreased sensation, and 2 is full sensation. Each side of the body is graded independently.
Complete and incomplete injuries
In a "complete" spinal injury, all functions below the injured area are lost, whether or not the spinal cord is severed. An "incomplete" spinal cord injury involves preservation of motor or sensory function below the level of injury in the spinal cord. To be classed as incomplete, there must be some preservation of sensation or motion in the areas innervated by S4 to S5, including voluntary external anal sphincter contraction. The nerves in this area are connected to the very lowest region of the spinal cord, and retaining sensation and function in these parts of the body indicates that the spinal cord is only partially damaged. Incomplete injury by definition includes a phenomenon known as sacral sparing: some degree of sensation is preserved in the sacral dermatomes, even though sensation may be more impaired in other, higher dermatomes below the level of the lesion. Sacral sparing has been attributed to the fact that the sacral spinal pathways are not as likely as the other spinal pathways to become compressed after injury due to the lamination of fibers within the spinal cord.Spinal cord injury without radiographic abnormality
exists when spinal cord injury is present but there is no evidence of spinal column injury on radiographs. Spinal column injury is trauma that causes fracture of the bone or instability of the ligaments in the spine; this can coexist with or cause injury to the spinal cord, but each injury can occur without the other. Abnormalities might show up on magnetic resonance imaging, but the term was coined before MRI was in common use.Central cord syndrome
, almost always resulting from damage to the cervical spinal cord, is characterized by weakness in the arms with relative sparing of the legs, and spared sensation in regions served by the sacral segments. There is loss of sensation of pain, temperature, light touch, and pressure below the level of injury. The spinal tracts that serve the arms are more affected due to their central location in the spinal cord, while the corticospinal fibers destined for the legs are spared due to their more external location.The most common of the incomplete SCI syndromes, central cord syndrome usually results from neck hyperextension in older people with spinal stenosis. In younger people, it most commonly results from neck flexion. The most common causes are falls and vehicle accidents; however other possible causes include spinal stenosis and impingement on the spinal cord by a tumor or intervertebral disc.
Anterior spinal artery syndrome
also known as anterior spinal cord syndrome, due to damage to the front portion of the spinal cord or reduction in the blood supply from the anterior spinal artery, can be caused by fractures or dislocations of vertebrae or herniated disks. Below the level of injury, motor function, pain sensation, and temperature sensation are lost, while sense of touch and proprioception remain intact. These differences are due to the relative locations of the spinal tracts responsible for each type of function.Brown-Séquard syndrome
occurs when the spinal cord is injured on one side much more than the other. It is rare for the spinal cord to be truly hemisected, but partial lesions due to penetrating wounds or fractured vertebrae or tumors are common. On the ipsilateral side of the injury, the body loses motor function, proprioception, and senses of vibration and touch. On the contralateral of the injury, there is a loss of pain and temperature sensations. If the injury is above pyramidal decussation there is contralateral hemiplegia, at the level of decussation there is completed motor loss on both sides and below pyramidal decussation there is ipsilateral hemiplegia.Spinothalamic tracts are in charge for pain and temperature sensation and because these tracts cross to the opposite side and above the spinal cord there is loss on the contralateral side.
Posterior spinal artery syndrome
, in which just the dorsal columns of the spinal cord are affected, is usually seen in cases of chronic myelopathy but can also occur with infarction of the posterior spinal artery. This rare syndrome causes the loss of proprioception and sense of vibration below the level of injury while motor function and sensation of pain, temperature, and touch remain intact. Usually posterior cord injuries result from insults like disease or vitamin deficiency rather than trauma. Tabes dorsalis, due to injury to the posterior part of the spinal cord caused by syphilis, results in loss of touch and proprioceptive sensation.Conus medullaris and cauda equina syndromes
syndrome is an injury to the end of the spinal cord the conus medullaris, located at about the T12–L2 vertebrae in adults. This region contains the S4–S5 spinal segments, responsible for bowel, bladder, and some sexual functions, so these can be disrupted in this type of injury. In addition, sensation and the Achilles reflex can be disrupted. Causes include tumors, physical trauma, and ischemia. Cauda equina syndrome may also be caused by central disc prolapse or slipped disc, infections such as epidural abscess, spinal haemorrhages, secondary to medical procedures and birth abnormalities.Cauda equina syndrome results from a lesion below the level at which the spinal cord ends. Descending nerve roots continue as the cauda equina at levels L2–S5 below the conus medullaris before exiting through intervertebral foraminae. Thus it is not a true spinal cord syndrome since it is nerve roots that are damaged and not the cord itself; however, it is common for several of these nerves to be damaged at the same time due to their proximity. CES can occur by itself or alongside conus medullaris syndrome. It can cause low back pain, weakness or paralysis in the lower limbs, loss of sensation, bowel and bladder dysfunction, and loss of reflexes. There may be bilateral sciatica with central disc prolapse and altered gait. Unlike conus medullaris syndrome, symptoms often occur only on one side of the body. The cause is often compression, e.g. by a ruptured intervertebral disk or tumor. Since the nerves damaged in CES are actually peripheral nerves because they have already branched off from the spinal cord, the injury has better prognosis for recovery of function: the peripheral nervous system has a greater capacity for healing than the central nervous system.